1. Field of the Invention
The present invention relates to the field of power management. More specifically, the present invention relates to the field of programmable power management in a programmable analog circuit containing an operational amplifier.
2. Related Art
A microcontroller is a highly integrated chip having all or most of the necessary components to control some process or aspect in a circuit. For example, the microcontroller typically includes a central processing unit (CPU), random access memory (RAM), read only memory (ROM), input/output (I/O) interfaces, timers, and interrupt controller. The typical microcontroller has bit manipulation instructions, easy and direct access to I/O interfaces, and quick and efficient interrupt processing. By including only features specific to the task of the microcontroller and integrating the functionality onto a single chip, the cost to produce the microcontroller can be drastically reduced.
Programmable analog circuit designs for microcontrollers allow a user limited programmability to vary circuit parameters or the underlying topology of the programmable analog circuit. For example, a programmable analog circuit may be comprised of interconnected analog blocks set in a fixed topology that has programmable parameters, such as filter bandwidth or roll-off, that can be set and changed according to application needs. While the signal processing path and basic functionality of the analog circuit remains unchanged, some programmable functionality is introduced by letting parameters vary in the programmable analog circuit.
A particular functionality important to programmable analog circuit designs is power management. Power management is particularly important in light of the movement towards higher levels of integration, and higher circuit densities. Programmable analog circuit blocks include basic programmable operational amplifier circuits used for many functionalities including gain amplifiers, switch capacitor integrators, analog to digital (A/D) converters, digital to analog (D/A) converters, filters, etc. In addition, a switched capacitor integrator forms the basis for an analog processing unit that can support A/D and D/A digital converters, comparators, programmable gain amplifiers, and filters.
As end products become more lightweight, smaller, and more portable, the microcontrollers operating at three volts and lower allow for less power consumption and longer battery life. However, in the past, designing the proper analog circuitry for lower power consumption was difficult to achieve without sacrificing operating performance. As a result, microcontrollers previously offered nonexistent or limited power management functionality.
FIG. 1 is a circuit diagram of the prior art illustrating a typical operational amplifier circuit used in analog circuits. Current sources 110 are biased with a bias voltage (not shown) in order to provide current to the operational amplifier circuit 100 that drives the output voltage and corresponding power coming out of the node 120. A compensation capacitor may be coupled between the nodes 120 and 130, and forms part of the load being driven by the operational amplifier circuit 100.
The current sources 110 are non-adjustable or not programmable. In the design illustrated in FIG. 1, the current sources are an unchangeable element in the output voltage and power shown at the node 120. As a result, there is no programmable power management in the current sources 110 for the operational amplifier circuit 100. For instance, the operational amplifier circuit 100 would consume the same amount of power irrespective of the load being driven.
One method implemented in the past for controlling power management throughout a programmable analog circuit included increasing or decreasing the bias voltage (not shown in FIG. 1). The bias voltage drives the operational amplifier circuit 100 in an programmable analog block. Increasing the bias voltage does increase the speed of the operational amplifier circuit 100 and the overall circuit; however, the improvement comes at a cost of performance.
Increasing the bias voltage increases the current through the operational amplifier in the programmable analog circuit. More current increases the slew rate of the programmable analog block and increases the operational amplifiers ability to drive the capacitor representative of the load. This allows the operational amplifier to run faster resulting in better performance.
However, there is a tradeoff. By increasing the bias voltage, the dynamic range of the operational amplifier is reduced. Basically, the dynamic range of output voltage at node 120 is clipped or reduced for the programmable analog block containing the operational amplifier. As a result, increasing the bias voltage negatively decreases the dynamic range of the block containing the operational amplifier.
Conversely, to maintain the dynamic range of the programmable analog block, the bias voltage (not shown) must be reduced. However, at the lower bias levels (and hence lower bias voltages, such as, three volts), the circuit containing the operational amplifier operates at much slower speeds.
Thus, a need exists to provide a degree of programmability to power management in a programmable analog circuit. Another need exists to provide increased speeds in a programmable analog circuit without sacrificing performance.